U.S. patent number 4,196,994 [Application Number 05/861,654] was granted by the patent office on 1980-04-08 for desensitized photoelectric detector unit.
This patent grant is currently assigned to Polaroid Corporation. Invention is credited to Charles de Jesus, William Hudspeth.
United States Patent |
4,196,994 |
de Jesus , et al. |
April 8, 1980 |
Desensitized photoelectric detector unit
Abstract
A photo-electric pulse generating unit for monitoring the focus
position of a camera objective lens driven in response to a range
detection system and operative to generate pulses on rotation of a
lens coupled encoder wheel having angularly spaced apertures
movable in relation to a detector unit housing the photo-electric
pulse generating unit. The unit mounts a pulse generating
photo-transistor in alignment with a light source such that the
photo-transistor is spaced behind an opaque wall opening to
"tunnel" light from a light source upon passing through an aperture
in the encoder wheel. Light diffusing surface irregularities are
provided to prevent impingement of reflected or ambient light on
the photo-transistor.
Inventors: |
de Jesus; Charles (Lexington,
MA), Hudspeth; William (Norwell, MA) |
Assignee: |
Polaroid Corporation
(Cambridge, MA)
|
Family
ID: |
25336397 |
Appl.
No.: |
05/861,654 |
Filed: |
December 19, 1977 |
Current U.S.
Class: |
396/133;
250/231.14; 250/239; 359/601 |
Current CPC
Class: |
G01D
5/34715 (20130101); G02B 7/40 (20130101) |
Current International
Class: |
G01D
5/26 (20060101); G01D 5/347 (20060101); G02B
7/40 (20060101); G01D 005/34 (); G02B 027/00 ();
G03B 003/00 (); H01J 005/02 () |
Field of
Search: |
;354/25,31,195
;350/271,273,275,276SL ;352/140 ;324/175 ;250/231SE,239 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Leinert et al. Stray Light Suppression in Optical Space
Experiments, Applied Optics Mar. 1974, pp. 556-564. .
Halter, E. A. Photoemitter for Recording Information, IBM Tech.
Disclosure Bulletin, Mar. 1967, pp. 1374-1375..
|
Primary Examiner: Gellner; Michael L.
Assistant Examiner: Tarcza; Thomas H.
Attorney, Agent or Firm: Thornton; David R.
Claims
What is claimed is:
1. In a camera having an automatic focusing system by which a lens
is displaced to various focusing positions and which includes a
pulse generating feedback system to monitor focusing movement of
the lens mount from its prior position, said feedback system
including an encoder member coupled to the lens for movement
therewith, said encoder member having a plurality of spaced
openings formed therein, and a detector including a light source
and a light sensitive element positioned on opposite sides of said
encoder member so that a pulse is generated in said detector upon
the passage of each of said spaced openings between said light
source and said element, the improvement wherein said detector unit
further comprises a generally U-shaped housing comprising first and
second hollow leg portions joined at one end by a base portion and
projecting therefrom to respectively support said light source and
said element, said hollow leg portions having a cavity extending
the length thereof for permitting slidable insertion of said light
source and said element through the base ends of said leg portions
and to a location adjoining the extended ends thereof, said first
and second leg portions presenting first and second spaced opaque
walls respectively with mutually facing wall surfaces, each of said
walls having a light passageway formed therein in alignment with
each other and with said light source and said element, and said
surface of said second wall facing said first wall is formed with
light diffusing irregularities alongside of the passageway
therethrough so as to diffuse source light reflected from the
encoder member or other portions of the system and prevent passage
of such reflected light to said element located in said second leg
behind said second wall.
2. The apparatus recited in claim 1 wherein said light diffusing
surface irregularities comprise linear striations aligned
transverse the direction of encoder movement.
3. The apparatus recited in claim 1 wherein said source and said
element each respectively carry at least one electrical lead, said
leads being extended through respective said hollow legs to at
least said base of said detector.
4. In a camera having an automatic focusing system by which a lens
is displaced to various focusing positions and which includes a
pulse generating feedback system to monitor focusing movement of
the lens mount from its prior position, said feedback system
including an encoder member coupled to the lens for movement
therewith, said encoder member having a plurality of spaced
openings formed therein, and a detector including a light source
and a light sensitive element positioned on opposite sides of said
encoder member so that a pulse is generated in said detector upon
the passage of each of said spaced openings between said light
source and said element, the improvement wherein said detector unit
further comprises a generally U-shaped housing comprising first and
second hollow leg portions joined at one end by a base portion and
projecting therefrom to respectively support said light source and
said element, said hollow leg portions having a cavity extending
the length thereof for permitting slidable insertion of said light
source and said element through the base ends of said leg portions
and to a location adjoining the extended ends thereof, said first
and second leg portions presenting first and second spaced opaque
walls respectively with mutually facing wall surfaces, each of said
walls having a light passageway formed therein in alignement with
each other and with said light source and said element, and said
light source has a given height, as measured in a direction
parallel to its principal optical axis, which at least equals the
height of the cavity in said first hollow leg, and said light
passageway in said first wall is an elongated slot extending along
the length of said leg to said base such that said source may be
placed in its operative position by sliding said source along said
hollow leg with the tip of said source extending within said
slot.
5. The apparatus of claim 4 wherein said element is supported
within said second leg portion on the opposite side of said second
wall from said first wall and spaced a distance from said second
wall to shield said element from light other than that emitted by
said light source and transmitted through the spaced openings in
said encoder member.
Description
BACKGROUND OF THE INVENTION
This invention relates to automatic lens focusing mechanisms for
photographic cameras and more particularly, it concerns an improved
photoelectric pulse generating unit for monitoring the focus
position of a camera objective lens driven in response to a range
detection system.
In a commonly assigned co-pending application Ser. No. 729,289,
filed Oct. 4, 1976, in the name of Edwin K. Shenk, and now
abandoned, there is disclosed a camera lens focusing mechanism in
which an electronic logic circuit responds to a range signal
related directly to the camera-subject distance in a manner to
produce a train of pulses, the number of which is representative of
the lens mount axial position at which the subject will be in
focus. Such pulses are gated into a counter and used for operating
a drive motor coupled mechanically to the lens mount. The lens
mount is coupled rotatably with an encoder wheel, operative as a
component of an auxiliary pulse generator in a feed-back systen, so
that operation of the lens drive motor causes the auxiliary pulse
generator to produce a predetermined number of pulses for each
axial unit displacement of the lens mount. The logic circuit
responds to the output of the auxiliary pulse generator to
determine when the lens mount has been moved to the position
determined by the pulse train counter to be proper for focusing the
subject to be photographed. Such logic circuit response results in
engagement of a pawl with a lens coupled rack to stop movement of
the lens mount at the proper focusing position even though the
drive motor may continue to rotate. A slip clutch in the coupling
between the motor and the lens mount facilitates this latter
operating characteristic.
In the feed-back system disclosed in the aforementioned copending
application, the pulses corresponding to lens displacement from a
pre-established position are preferably generated by rotation of
slots or apertures in the lens encoder wheel between a light
source, such as a light emitting diode (LED) and a photocell. The
increments of angular spacing between the slots or apertures in the
encoder wheel are directly related to increments of lens mount
rotation which, because of a pre-established thread or camming
pitch of the lens mount, represent axial increments of lens
focusing movement. This arrangement has a distinct advantage from
the standpoint of elimination of frictional or mechanical drag on
movement of the lens mount to appropriate focusing positions and as
well, it is easily adaptable to electronic circuitry suited for
automatic focusing systems.
There are, however, problems presented from the standpoint of the
size of the photo-electric feed-back system capable of being
accomodated in a viable automatic focusing camera design, facility
for assembly in the shutter housing of a camera, calibration of
photocell generated pulses with lens mount movement from a given
reference position, and elimination of erratic pulse generation due
to exposure of the photocell to stray light.
SUMMARY OF THE PRESENT INVENTION
In accordance with the present invention, an improved photoelectric
detector unit is provided for use particularly with the encoder
wheel of automatic focusing systems of the afore-mentioned type and
by which problems associated with faulty pulse generation as a
result of stray light are substantially alleviated. The detector is
a self-contained unit having an integral, opaque housing shaped to
establish a pair of hollow leg portions for receiving respectively,
a light source such as an LED and a photo-transistor; each of which
is positioned to lie on opposite sides of an apertured encoder
wheel. The photo-transistor is spaced behind an opaque wall having
a slot through which light passes from the LED. In addition,
potentially reflective surfaces on the unit housing are provided
with light diffusing striations as a further protection against
stray light reaching the photo-transistor.
Accordingly, among the objects of the present invention are; the
provision of an improved photoelectric pulse generating unit
particularly, though not exclusively, adapted for use in cameras
equipped with automatic focusing systems; the provision of such a
detector which may be fabricated as a unit to facilitate its
assembly; the provision of such a detector in which sensitivity may
be maximized without potential for false signal generation; and the
provision of a physical structural configuration for such detectors
which facilitates miniaturized components.
Other objects and further scope of applicability of the present
invention will become apparent from the detailed description to
follow taken in conjunction with the accompanying drawings in which
like parts are designated by like reference numerals.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary cross-section or cutaway side elevation of
a camera incorporating the present invention;
FIG. 2 is an enlarged fragmentary cross-section on line 2--2 of
FIG. 1;
FIG. 3 is a similarly enlarged fragmentary cross-section on line
3--3 of FIG. 1;
FIG. 4 is an enlarged front elevation illustrating the detector
unit of the present invention;
FIG. 5 is a cross-section on line 5--5 of FIG. 4; and
FIG. 6 is a cross-section on line 6--6 of FIG. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1 of the drawings, a camera incorporating the present
invention is shown to include an exterior casing 10 having a front
wall 12 through which an objective lens is presented and generally
designated by the reference numeral 14 in FIG. 1. The particular
embodiment of the camera illustrated is intended as an adaptation
of a well-known commercially available camera of the type in which
the upper sheet of a film pack (not shown) is presented at a film
plane 17 in a light-tight chamber 16 and processed after exposure
by withdrawal through pressure rollers or bars (not shown) at the
front of the camera. Supported in the chamber 16 is a mirror 18 by
which light passing along the optical axis 20 of the lens 14 is
reflected downwardly to the film plane as is well-known in the art.
Also, a rearwardly extending viewfinder tube 22 extends from the
rear of the exterior casing 10.
The chamber 16 is delineated at its front edge by a wall 24 having
an aperture 26 therein centered on the optical axis 20 and
positioned directly behind a shutter blade set 28. The several
components of the exposure control system by which the shutter
blades 28 are conventionally operated are omitted from the drawings
in the interest of more clearly illustrating a structural
embodiment of the present invention. Such components, however, will
be located in the space between the walls 12 and 30 or within the
"shutter housing", a term for the enclosure of such space and
designated in FIG. 1 by the reference numeral 29.
Supported within the housing 29, forwardly of the shutter blades
28, is a lens board 30 for supporting the stationary components of
the lens 14. In this respect, it will be noted that the lens
illustrated is a three-element lens in which two stationary lens
elements 32 and 34 are fixed in a cylindrical mount 36, having a
rear extension 38 of reduced diameter extending through an
appropriately reinforced opening 40 in the lens board 30, and
secured permanently against movement relative to the lens board by
appropriate means such as ultrasonic fusion, a self-locking spring
washer or the like.
The fixed lens mount 36 supports a forwardly projecting, internally
threaded cylindrical portion 42 adapted to receive an externally
threaded cylindrical portion 44 of a movable lens mount 46 which
carries a movable lens element 48. The lens system and mount, as
thus described, are conventional and operate to focus a subject
image on the film plane 17 upon rotation of the mount 46 to adjust
the lens element 48 inwardly or outwardly relative to the element
34. Specifically, an "infinity" adjustment of the lens 14, in which
subjects beyond a camera-subject range of approximately 7-9 meters
will be in focus, is effected when the lens element 48 is adjusted
rearwardly to a pre-established position near the element 34.
Subjects at closer range than this from the camera will be brought
into focus by rotation of the mount 46 in a direction to move the
element 48 away from the element 34. Although such focusing
adjustments of the lens 14 are conventionally made by manually
rotating the lens mount 46 relative to the stationary lens mount
36, usually with the aid of either camera-subject distance
calibrations on the mount 46 or with the aid of an optical range
finder provided in conjunction with the viewing tube 22, the camera
embodiment illustrated in FIG. 1 is adapted for use with an
automatic ranging system including an electric drive motor 50. The
automatic ranging system for operating the motor 50 is not shown in
the drawings nor is a description thereof believed necessary for a
complete understanding of the present invention. Acceptable
electronic ranging systems are disclosed in U.S. Pat. No. 3,522,764
as well as in the above-mentioned copending application Ser. No.
729,289, the latter being incorporated herein by reference to the
extent that the disclosure thereof is necessary for one skilled in
the art to practice the present invention.
The manner in which the lens mount 46 is coupled for rotation by
operation of the motor 50 may be understood by reference to FIGS.
1-3 of the drawings. As shown most clearly in FIG. 1, the lens
mount 46 is provided with a rearwardly extending cylindrical sleeve
52 having a longitudinal exterior keyway 54 or equivalent. The
sleeve 52 is slidably received within a ring 56 having a tang 58
slidable in the keyway 54. The ring 56 is externally journalled for
rotation in an apertured support wall 60 positioned forwardly of
the lens board 30 in a manner such that it is retained against
axial movement during rotation. In this latter respect, the ring 56
is provided at its rear end with a flange 62 having rack teeth 64
provided thereon. At the forward end of the ring 56, an outwardly
projecting encoder wheel 66 is mounted by fusion or the like and in
a manner to capture the apertured journal portion of the wall 60 to
prevent axial displacement of the ring 56. The encoder ring 66 is
provided with external gear teeth 68 for engagement by a gear 70
coupled to the motor 50 by way of a slip clutch 72. In light of
this organization it will be appreciated that operation of the
motor to rotate the gear 70, will rotate the encoder wheel 66 and
ring 56 to rotate the lens mount 46 as a result of the key slot 54
and tab 58. Rotation of the lens mount 46 in this manner will not
impede axial displacement of the mount and the lens element 48 as a
result of the threaded interconnection of the cylindrical portions
42 and 44.
As described in the afore-mentioned co-pending application Ser. No.
729,289, the logic circuitry of the automatic focusing system
disclosed therein, provides appropriate controls by which the motor
50 may be energized to rotate the encoder wheel 66 and the lens
mount 46, preferably from its position of infinity, until a subject
to be photographed is in focus on the film plane 17 as a result of
a range detection facility provided by the system. A determination
of when the lens mount has been moved through the appropriate
position for focus is determined by an auxiliary pulse generator
associated with the lens coupled encoder wheel. In the disclosed
embodiment, therefore, the encoder wheel 66 is provided with a
series of openings 74 spaced angularly by opaque wheel portions 76
and located to pass in light passing and blocking relationship to a
photocell detector unit 78 (See FIG. 3). A solenoid actuated pawl
mechanism 80 (FIG. 2) is positioned to engage the rack teeth 64 on
the ring 56 to latch the movable lens mount 46 in a properly
focused position after the appropriate number of openings 74 have
passed the detector unit 78 and generated a corresponding number of
auxiliary pulses.
Although the function and operation of the photoelectric detector
78 in the electronic circuitry of the automatic focusing system
incorporated in the shutter housing 29 is fully disclosed in the
afore-mentioned co-pending application, the physical structure of
the detector 78 is important for reliable generation of auxiliary
pulses resulting solely from movement of the encoder wheel during
the lens focusing adjustment. As shown most clearly in FIGS. 4-6 of
the drawings, the detector 78 is a self-contained unit, and as
such, includes an integral housing 80 of generally U-shaped
configuration to define a base portion 82 from which a pair of leg
portions 84 and 86 extend to be positioned on opposite sides of the
apertured flange configuration of the encoder wheel 66. The housing
or casing 80 is preferably a molding of appropriate synthetic
resinous material and is hollow to establish in the leg 84, a
photo-transistor (light receiving) chamber 88 and an LED (light
sending) chamber 90 in the leg 86, respectively. In the respective
chambers 88 and 90 are mounted a photosensitive element 94 such as
a photocell or preferably, a photo-transistor and a light source 92
such as an LED. Advantageously, electrical leads 93 and 95 of the
light source 92 and the element 94 extend the length of their
respective hollow legs to the hollow base 82 from which appropriate
circuit connections may be made.
As shown more clearly in FIGS. 4 and 5, the leg portions 84 and 86
establish opaque walls 96 and 98 to present mutually facing
parallel wall surfaces 100 and 102 to be positioned on opposite
sides of the encoder wheel 66. The wall 96 of the receiving chamber
88 is provided with a small, light receiving aperture 104 centered
on an axis 106 perpendicular to both the wall surfaces 100 and 102.
The wall 98 is formed with an elongated central slot 108 through
which light from the LED 92 is transmitted to the aperture 104 and
the photo-transistor 94. The elongated slot 108 extends from the
base portion 82 so that the source 92 may be slid to its forward
position, as shown, at the end of the hollow leg 86 without
engagement of the tip of the source 92 with the wall 98. That is,
for compactness, the height of the hollow leg 86 is less than the
height of the light source 92, however, the elongated slot
facilitates insertion of the source while also transmitting light
from the source 92 to the receiver in the other leg.
It will be noted in FIGS. 4 and 5 that the photo-transistor 94 is a
thin, wafer-like element supported against the interior wall
surface of the leg 84 remote from the wall 96 in which the light
receiving aperture 104 is formed, and the light concentrating
lenses normally provided in the encapsulating housing of
photo-transistors are removed such that the light receiving surface
of the photo-transistor is presented directly and exclusively to
light passing from the LED 92. The material of which the detector
unit is made is preferably opaque, although in a strict sense only
the leg 84 need be made of opaque material so as to protect the
receiving element 94 from ambient illumination. In addition, all
interior surfaces of the leg 84 are a dull, relatively
non-reflecting black and the entrance to this hollow leg is light
sealed as by plastic potting compound such that the potential for
light other than that emitted by the LED 92 reaching the photocell
94 is reduced to a minimum.
The undesirable effects of stray light reaching the photocell 94
are further mitigated by the provision of light diffusing
striations embossed in the surface 100 of the wall 96 in which the
light receiving aperture 104 is provided. The striations in the
surface 100 not only diffuse light from sources other than the LED
92, but also prevent the reflection of light around the opaque
portions 76 of the encoder wheel which exist between the light
passing openings 74. In other words, light passing from the LED 92,
upon striking a surface portion of the encodeer wheel other than an
area in which an aperture 74 is located, if reflected against the
wall surface 100, will be diffused without passage to the
photo-transistor 94. As a result of this construction of the
detector unit 78, the photo-transistor can be selected to be
extremely sensitive and capable of generating strong, distinct
auxiliary pulses each time an opening 74 in the encoder wheel
passes the axis 106.
Thus it will be appreciated that as a result of the present
invention a highly effective photoelectric detector structure is
provided by which the above-mentioned objectives are completely
fulfilled. Since it will be apparent to those skilled in the art
that various changes and/or modifications may be made in the
disclosed embodiment without departure from underlying inventive
concepts, it is expressly intended that the foregoing description
is illustrative of a preferred embodiment only, not limiting, and
that the true spirit and scope of the present invention be
determined by reference to the appended claims.
* * * * *